1. Field of Invention
The present invention relates to a solar cell module.
2. Description of Related Art
Owing to the shortage of fossil fuels, awareness of the importance of environmental protection is increasing. Therefore, many have been actively developing technologies related to alternative energy and renewable energy in recent years, with the hope that the dependence on fossil fuels and the impact on the environment caused by using fossil energy can be reduced. Among the various kinds of technologies related to alternative energy and renewable energy, the solar cell is a technology that is receiving much attention. The reason for the interest in this technology is that solar cells can directly convert solar energy into electricity, and carbon dioxide or other harmful substances such as nitrogen compounds will not be produced during the process of power generation, so that the environment will not be polluted.
Silicon is the most important and widely used material in the semiconductor industry. Today, the technologies behind the production and supply of silicon wafers are already at a quite mature stage. The energy gap of silicon is suitable for absorbing sunlight, and it is for at least this reason that silicon solar cells have become the most widely used solar cells. Generally, a monocrystalline silicon solar cell or a polycrystalline silicon solar cell includes the layers of an external electrode, an anti-reflective layer, an n-type semiconductor layer, and a p-type semiconductor layer.
Generally, the material of the external electrode is a combination of various metals, such as nickel, silver, aluminum, copper, and palladium. In order to maintain a sufficient electron flow, the transmission area between the electrodes and the substrate must be adequately large. However, in order to reduce the shielding rate of an external electrode with respect to incident light, the area that the external electrode covers on the substrate must be as small as possible. Therefore, the structural design of the external electrode must take into account properties such as low resistance and low light-shielding rate. Currently available external electrodes can be divided into sections of bus bar electrodes and finger electrodes. A cross-sectional area of the bus bar electrode is larger than a cross-sectional area of the finger electrode. If the structure of a tree is used as a comparison, the bus bar electrode is like the trunk of the tree, and the finger electrodes are like branches of the tree spreading on the surface of the whole solar cell. The electrons will converge toward the bus bar electrode via the finger electrodes and then toward the external load. That is to say, the bus bar electrode with its larger size will help to improve the electron flow, and the finger electrodes with their smaller size will help to reduce the light-shielding rate.
In a currently available solar cell, there are either two or three bus bar electrodes on each of the first surface and the second surface of the solar cell. While a solar cell that has two bus bar electrodes on each of the first surface and the second surface has a lower light-shielding rate than a solar cell that has three bus bar electrodes on each of the first surface and the second surface, the energy loss of the former type of solar cell is larger than the energy loss of the latter type of solar cell. Therefore, many in the field are endeavoring to design a solar cell in such a manner to decrease the energy loss without increasing the light-shielding rate of the solar cell.